Nanoelectromechanical systems utilizing nanometer-scale assemblies that convert thermal energy into another form of energy that can be used to perform useful work at a macroscopic level are described in U.S. Pat. No. 7,148,579 to Pinkerton et al. (“the '579 Patent,” which is incorporated herein by reference in its entirety). Such systems can be used to produce useful quantities of electric or mechanical energy, heat or cool an external substance or propel an object in a controllable direction. The '579 Patent system included nanometer-scale beams that reduced the velocity of working substance molecules that collide with this nanometer-scale beam by converting some of the kinetic energy of a colliding molecule into kinetic energy of the nanometer-scale beam. For instance, FIGS. 24 and 25 of the '579 Patent illustrated piezoelectric generators parallel and in series for converting thermal motion into an electric output. However, the piezoelectric elements of the '579 Patent may be too large to experience thermal oscillations of sufficient magnitude to open and close a nearby electrical contact. Also, van der Waals forces may cause the free end of these elements to get stuck to its nearby electrical contact.
Piezoelectric nanowires, such as ZnO nanowires, are described in Gao et at, Nano Lett., 2009, 9(3), 1103-1110 (“Gao,” which is incorporated herein by reference in its entirety). As taught in Gao, when a nanowire bends one way and produces positive charge, this charge may be milled by mobile electrons. When that nanowire bends the other way and produces negative charge, the mobile electrons do not screen, so the system produces a net negative voltage. This is in contrast to piezoelectric energy conversion devices that produce positive/negative charge in equal amounts for opposite deflections.